Finnish published patent application No. 49574 and German published patent application OS No. 1,934,359 disclose boxes privided with a tear strip or a tear flap. When erecting these boxes the blank of the inner part is first turned against the inner side of the blank of the outer part and then the box is formed by folding both blanks together along the longitudinal fold lines of the box. A disadvantage of the above mentioned boxes is the fact that the outer sides of the inner part and outer part of the box, i.e. the panels to be printed, are located on opposite sides of the blank. Therefore the blank has to be printed or surface-treated on both sides.
U.S. Pat. No. 4,083,454 discloses a two-piece box which has been formed by folding the blank of the box along the longitudinal fold lines of the box in the same direction. The inner part of the box is detached from the outer part by removing a tear strip connecting the parts. Due to the structure of the box, the mantle-like outer part is opened when the tear strip is removed.
Finnish published patent application No. 54252 discloses a two-piece box which has been formed by folding the blank of the inner part and the blank of the outer part successively in the same direction. The mantle-like inner part and the outer part of the box are detached from each other by subjecting force onto the weakened line connecting them. As the detachment requires special tools, it has to be carried out before the box is delivered to the user.